The present invention relates to a microstructure and its manufacturing method.
In the technical field of metal and semiconductor thin films, wires and dots, it is known that the movement of free electrons becomes confined at sizes smaller than some characteristic length, as a result of which singular electrical, optical and chemical phenomena become observable. Such phenomena are called “quantum mechanical size effects” or simply “quantum size effects.” Functional materials which employ such singular phenomena are under active research and development. Specifically, materials having structures smaller than several hundred nanometers in size, typically called microstructures or nanostructures, are the subject of current efforts in material development.
Methods for manufacturing such microstructures include processes in which a nanostructure is directly manufactured by semiconductor fabrication technology, including micropatterning technology such as photolithography, electron beam lithography, or x-ray lithography.
Of particular note is the considerable amount of research being conducted today on processes for manufacturing nanostructures having an ordered microstructure.
One method of forming an ordered structure in a self-regulating manner is illustrated by an anodized alumina film (anodized film) obtained by subjecting aluminum to anodizing treatment in an electrolytic solution. It is known that a plurality of micropores having diameters of about several nanometers to about several hundreds of nanometers are formed in a regular arrangement within the anodized film. It is also known that when a completely ordered arrangement is obtained by the self-pore-ordering treatment of this anodized film, hexagonal columnar cells will be theoretically formed, each cell having a base in the shape of a regular hexagon centered on a micropore, and that the lines connecting neighboring micropores will form equilateral triangles.
Known examples of applications for such anodized films having micropores include optical functional nanodevices, magnetic devices, luminescent supports and catalyst supports. For example, JP 2005-307341 A describes that an anodized film is applied to a Raman spectrometer by sealing pores with a metal and generating localized plasmon resonance.
JP 2005-156695 A describes that surface pores are subjected to a combination of anodizing treatment and pore widening treatment to produce an anodized porous alumina film in which pores have continuously changing diameters and are thus given tapered shapes.
A method is known in which pits serving as starting points for micropore formation in anodizing treatment are formed prior to anodizing treatment for forming such micropores. Formation of such pits facilitates controlling the micropore arrangement and variations in pore diameter within desired ranges.
A self-ordering method that makes use of the self-ordering nature in the anodized film is known as a general method for forming pits. This is a method which enhances the orderliness by using the regularly arranging nature of micropores in the anodized film and eliminating factors that may disturb an orderly arrangement.
As described in JP 2005-307341 A, the self-ordering method generally involves performing anodizing treatment, then immersion in a mixed aqueous solution of phosphoric acid and chromic (VI) acid, and thereafter performing anodizing treatment again.